1. Field of the Invention
This invention relates to a new process for preparing aromatic phosphine oxides which are useful as flame retardants for organic polymers.
2. Description of the Prior Art
Dorken, in Chem. Berichte (1888), 21, p. 1505-1515, teaches the preparation of aromatic phosphine oxides by a two-step process starting with diarylhalophosphine. Chlorodiphenylphosphine is reacted with benzyl chloride to yield benzyldiphenylphosphine dichloride in accordance with the following equation in which the symbol Ph is used to represent the phenyl radical: EQU Ph.sub.2 PCl + PhCH.sub.2 CL .fwdarw. PhCH.sub.2 PCl.sub.2 Ph.sub.2.
When this dichloride is hydrolyzed in water, benzylphenylphosphine oxide is obtained. EQU PhCH.sub.2 PCl.sub.2 Ph.sub.2 .sup.HOH PhCH.sub.2 P(O )Ph.sub.2.
Horner et at., in Chem. Berichte (1962), 95, p. 581-601, teach the two-step reaction: ##SPC3##
Somewhat related phosphine oxides have been prepared in a one-step process starting with an aliphatic phosphine oxide rather than a diarylhalophosphine. Rauhut et al., Jour. Org. Chem., vol. 26, p. 4628-4632 (1961), teach the reaction of bis(2-cyanoethyl) phosphine oxide with 2,4-dichlorobenzyl chloride in methanolic sodium hydroxide to give bis(2-cyanoethyl) (2,4-dichlorobenzyl)phosphine oxide. ##SPC4##